1. Field of the Invention
The present invention relates to the field of 3rd Generation (3G) mobile communication, especially to a registration request that is not initiated by a subscriber in an Internet Multimedia Sub-system.
2. Description of the Related Art
The Internet Multimedia Sub-system (IMS), as shown in FIG. 1, is a structural framework established by the 3rd Generation Partnership Project (3GPP) to provide subscribers with the IMS service. Before using the IMS service, a subscriber (user equipment) 101 must register with a Service Call Session Control Function (S-CSCF) 104 of the IMS, informing an S-CSCF subscriber of a binding relationship between a subscriber's Public User Identification (PUI) and an Internet Protocol (IP) address corresponding to the location of the subscriber. During the process of registration, the subscribers can also inform the network of their characteristics and the support ability and so on. (For more information, please refer to the criterion Technical Specification (TS) 23.228 of the 3GPP). In FIG. 1, a Proxy Call Session Control Function (P-CSCF) 102 serves as a proxy gateway for IMS accessing, which usually is a certain gateway of the network in which the subscriber currently locates. The address of the gateway is detected by the P-CSCF 102 and informed by the network when the subscriber is performing IP access. (For more information on how to implement the above operation, please refer to criterion TS23.228). By parsing a home network name included in the PUI of the subscriber 101, the P-CSCF 102 locates an Inquiry Call Session Control Function (I-CSCF) 103, through which the P-CSCF 102 can interact with a Home network registration Subscriber Server (HSS) 105 to locate the S-CSCF 104 that the subscriber 101 belongs to. After the I-CSCF 103 locates the subscriber's S-CSCF 104, the I-CSCF 103 forwards messages received from the P-CSCF 102 to the S-CSCF 104 to process the messages. If the S-CSCF 104 has not already saved the subscriber's service attribute, the S-CSCF requests the subscriber's service attribute from the HSS 105. Some details on the interaction between the I-CSCF and the HSS and that the interaction between the S-CSCF and the HSS are illustrated in FIG. 9. The S-CSCF proceeds with processing messages received from the subscriber.
FIG. 9 shows a process of a registration state inquiry. In step 801, the I-CSCF receives an INVITE message, which is used to establish a first Session Initiation Protocol (SIP) message initiated by an IMS call. The INVITE message includes a subscriber's SIP Uniform Resource Identifier (URI) or TELephone (TEL) URI. Regardless of which subscriber's PUI is included in this message, the I-CSCF is able to locate the subscriber's HSS according to available criteria. In the HSS, information on some service characteristics and the like agreed upon between the subscriber and the operator is included. In addition, the information on whether the subscriber has registered with the IMS is included in the HSS. In step 802, the I-CSCF sends a (Location Query) Cx-LocQuery message to the HSS, including the subscriber's information on PUI, etc. In 803, the HSS returns the information on whether the subscriber has been registered, which is included in (Location Query Response) Cx-LocQueryResp message, If the subscriber has been registered, the HSS returns the selected S-CSCF information to the HSS. If the subscriber's S-CSCF information or the S-CSCF characteristic information for the subscriber is included in step 803, the I-CSCF selects a certain S-CSCF according to the characteristics of S-CSCF in step 804. In step 805, after the S-CSCF has been selected, the I-CSCF sends the received INVITE message to the S-CSCF. If the S-CSCF is unaware of the subscriber's service attributes, the S-CSCF requests the subscriber's service attribute information from the HSS. In step 806, the S-CSCF sends a Cx-Pull message to the HSS, including a User Equipment's (UE's) PUI, etc. In step 807, the HSS returns the subscriber's service attributes to the S-CSCF. According to the subscriber's service attributes information obtained in the previous step, the S-CSCF conducts a service control in step 808 and then performs a corresponding service operation in step 809.
On a basis of the IMS, the 3GPP is working on establishing a standard of Combinatorial Circuit Switching domain Call and IMS Session known as a Customer Information Control System (CICS) Socket Interface (CSI), which is also referred to in FIG. 8 for more information.
Two Circuit Switching (CS) and IMS clients are set in a User Equipment (UE), one client for a CS domain call, and the other client for a session of the IMS domain. When the CS domain call and the IMS domain session are conducted simultaneously between the same two UEs, then in the application layer of the UE, the same combinatorial service is presented to the subscriber by at least one Application Server (AS) connected the IMS domain. In this case, some interactions, operations, etc. between the CS domain and the IMS domain should occur.
In FIG. 8, the UEs access a CS domain core of the CS domain and an IMS domain core of the IMS domain through Access networks corresponding to each of the UEs. The CS domain core refers to the network entity related to the CS domain call. In general, the CS domain core may include a Mobile terminal Switching Center (MSC), a Visitor Location Register (VLR), etc. The IMS domain core refers to the network entity related to the IMS domain session. In general, it may include all entities in FIG. 1.
Before conducting a CSI service between two UEs, the two UE's must be informed of their abilities in CSI supporting in advance. The ability in CSI supporting is transferred via an OPTIONS message. FIG. 2 illustrates the process of transferring a terminal's CSI supporting ability between two subscribers through the OPTIONS message, which may include parameters such as UE A's MS-Integrated Services Digital Network (ISDN), the SIP URI, the type of media bearer, information regarding whether the CSI is supported, etc. Actually, in steps 201 to 203, UE A sends the OPTIONS message to UE B. The UE A is the mobile terminal currently used by the calling subscriber to initiate the call to the called subscriber; while UE B is the mobile terminal currently used by the called subscriber to receive the call from the calling subscriber. (For details on these parameters, please refer to criterion 3GPP TS 23.279). Then in steps 205 to 207, the UE B sends the 200 OK message to the UE A, which includes the UE B's MS-ISDN, the SIP URI, the type of media bearer, whether the CSI is supported, etc. In this way, the UE A knows about the UE B's terminal ability, and vice versa. In other words, in step 204, the UE B updates the UE A's ability that is saved in the UE B's memory, and in step 208 UE A updates the UE B's ability, which is saved in the UE A's memory. The terminal ability of the counterpart is saved in the terminal of the UE and is monitored and controlled by a certain timer. If timeout of the timer occurs, the timer begins to exchange a new process of terminal ability. In addition the terminal ability of the counterpart saved in the flash memory will be overwritten by a new one.
If the terminal ability of the counterpart is not saved in the UE A, the Circuit Switching domain call is initiated by the UE A between the UE A and the UE B. As shown in FIG. 3, in step 301, a CS domain call is conventionally established between a subscriber A and a subscriber B, and the communication is performed. In order to conduct the CSI subsequently, the process of terminal ability exchanging is performed between the subscriber A and the subscriber B. Step 302 in FIG. 3, contains all of the steps of FIG. 2. When the OPTIONS message is sent by the subscriber A to the subscriber A's S-CSCF, the message may include the information on the UE B's TEL URI as well as the subscriber A's terminal ability information. After this message is transferred from the UE A's S-CSCF to the IMS core B of the called UE B, the subscriber that has not registered with the IMS is detected, i.e., the IMS core B does not have the subscriber's current IP address. Therefore, communication between the UE A and the UE B cannot occur. Similarly, if the UE A knows the UE B's terminal ability, but the IMS core B detects that the subscriber has not registered with the IMS when the IMS session is being established in steps 303-314, i.e., the IMS core B does not have the subscriber's current IP address, communication between the UE A and the UE B cannot occur.